1. Field of the Invention
The present invention relates to a method for manufacturing an oxide superconductor thin film excellent in surface morphology.
2. Description of the Related Art
Since the discovery of oxide superconductors with high critical temperatures, researches on methods of manufacturing oxide thin films have greatly advanced. Hereinafter, the critical temperature will be referred to as "Tc". Of such methods, the most widely used is a method comprising the steps of applying a laser beam to a target made of an oxide material to evaporate the oxide material, and then depositing and accumulating the evaporated material on a substrate. In this method, since the thin film is formed in an atmosphere with a high oxygen partial pressure, oxygen can be incorporated sufficiently into the oxide thin film. Further, this method can easily form a thin film whose composition similar or substantially same to that of the target. Therefore, the formed film can be used as a superconductor film as it is without any further treatment.
However, in this method, a laser beam applied to a target at a high radiation energy density, possibly deteriorates the target. In addition, the thin film formed by this method have numerous particles of approximately 1 .mu.m in diameter on its surface, unlike thin films made by other methods such as a sputter method and a vacuum evaporation method. These particles markedly lower the surface morphology. In this case, when a plurality of films of poor surface morphology are laid one upon another to form a multi layered film or a laminated type junction, the interface between the layers becomes a non-homogeneous condition. Due to the non-homogeneous condition, it is difficult to accurately evaluate the properties of each of the formed thin films. Heretofore, many attempts have been made with a view toward reducing the particle generation.
In an attempt, a thin film was formed by a conventional method under such a condition as to reduce the density of particles being generated. However, the superconductivity of thus-formed film was found to have deteriorated. Heretofore, no methods for forming a thin film having both of an excellent morphology (a smooth surface) and superconductivity, have yet been proposed.